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// Copyright Joyent, Inc. and other Node contributors.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to permit
// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
// USE OR OTHER DEALINGS IN THE SOFTWARE.
#ifndef SRC_BASE_OBJECT_H_
#define SRC_BASE_OBJECT_H_
#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
#include <type_traits> // std::remove_reference
#include "memory_tracker.h"
#include "v8.h"
namespace node {
class Environment;
template <typename T, bool kIsWeak>
class BaseObjectPtrImpl;
namespace worker {
class TransferData;
}
class BaseObject : public MemoryRetainer {
public:
enum InternalFields { kSlot, kInternalFieldCount };
// Associates this object with `object`. It uses the 0th internal field for
// that, and in particular aborts if there is no such field.
inline BaseObject(Environment* env, v8::Local<v8::Object> object);
inline ~BaseObject() override;
BaseObject() = delete;
// Returns the wrapped object. Returns an empty handle when
// persistent.IsEmpty() is true.
inline v8::Local<v8::Object> object() const;
// Same as the above, except it additionally verifies that this object
// is associated with the passed Isolate in debug mode.
inline v8::Local<v8::Object> object(v8::Isolate* isolate) const;
inline v8::Global<v8::Object>& persistent();
inline Environment* env() const;
// Get a BaseObject* pointer, or subclass pointer, for the JS object that
// was also passed to the `BaseObject()` constructor initially.
// This may return `nullptr` if the C++ object has not been constructed yet,
// e.g. when the JS object used `MakeLazilyInitializedJSTemplate`.
static inline BaseObject* FromJSObject(v8::Local<v8::Value> object);
template <typename T>
static inline T* FromJSObject(v8::Local<v8::Value> object);
// Make the `v8::Global` a weak reference and, `delete` this object once
// the JS object has been garbage collected and there are no (strong)
// BaseObjectPtr references to it.
inline void MakeWeak();
// Undo `MakeWeak()`, i.e. turn this into a strong reference that is a GC
// root and will not be touched by the garbage collector.
inline void ClearWeak();
// Reports whether this BaseObject is using a weak reference or detached,
// i.e. whether is can be deleted by GC once no strong BaseObjectPtrs refer
// to it anymore.
inline bool IsWeakOrDetached() const;
// Utility to create a FunctionTemplate with one internal field (used for
// the `BaseObject*` pointer) and a constructor that initializes that field
// to `nullptr`.
static inline v8::Local<v8::FunctionTemplate> MakeLazilyInitializedJSTemplate(
Environment* env);
// Setter/Getter pair for internal fields that can be passed to SetAccessor.
template <int Field>
static void InternalFieldGet(v8::Local<v8::String> property,
const v8::PropertyCallbackInfo<v8::Value>& info);
template <int Field, bool (v8::Value::*typecheck)() const>
static void InternalFieldSet(v8::Local<v8::String> property,
v8::Local<v8::Value> value,
const v8::PropertyCallbackInfo<void>& info);
// This is a bit of a hack. See the override in async_wrap.cc for details.
virtual bool IsDoneInitializing() const;
// Can be used to avoid this object keepling itself alive as a GC root
// indefinitely, for example when this object is owned and deleted by another
// BaseObject once that is torn down. This can only be called when there is
// a BaseObjectPtr to this object.
inline void Detach();
static v8::Local<v8::FunctionTemplate> GetConstructorTemplate(
Environment* env);
// Interface for transferring BaseObject instances using the .postMessage()
// method of MessagePorts (and, by extension, Workers).
// GetTransferMode() returns a transfer mode that indicates how to deal with
// the current object:
// - kUntransferable:
// No transfer is possible, either because this type of BaseObject does
// not know how to be transferred, or because it is not in a state in
// which it is possible to do so (e.g. because it has already been
// transferred).
// - kTransferable:
// This object can be transferred in a destructive fashion, i.e. will be
// rendered unusable on the sending side of the channel in the process
// of being transferred. (In C++ this would be referred to as movable but
// not copyable.) Objects of this type need to be listed in the
// `transferList` argument of the relevant postMessage() call in order to
// make sure that they are not accidentally destroyed on the sending side.
// TransferForMessaging() will be called to get a representation of the
// object that is used for subsequent deserialization.
// The NestedTransferables() method can be used to transfer other objects
// along with this one, if a situation requires it.
// - kCloneable:
// This object can be cloned without being modified.
// CloneForMessaging() will be called to get a representation of the
// object that is used for subsequent deserialization, unless the
// object is listed in transferList, in which case TransferForMessaging()
// is attempted first.
// After a successful clone, FinalizeTransferRead() is called on the receiving
// end, and can read deserialize JS data possibly serialized by a previous
// FinalizeTransferWrite() call.
enum class TransferMode {
kUntransferable,
kTransferable,
kCloneable
};
virtual TransferMode GetTransferMode() const;
virtual std::unique_ptr<worker::TransferData> TransferForMessaging();
virtual std::unique_ptr<worker::TransferData> CloneForMessaging() const;
virtual v8::Maybe<std::vector<BaseObjectPtrImpl<BaseObject, false>>>
NestedTransferables() const;
virtual v8::Maybe<bool> FinalizeTransferRead(
v8::Local<v8::Context> context, v8::ValueDeserializer* deserializer);
// Indicates whether this object is expected to use a strong reference during
// a clean process exit (due to an empty event loop).
virtual bool IsNotIndicativeOfMemoryLeakAtExit() const;
virtual inline void OnGCCollect();
private:
v8::Local<v8::Object> WrappedObject() const override;
bool IsRootNode() const override;
static void DeleteMe(void* data);
// persistent_handle_ needs to be at a fixed offset from the start of the
// class because it is used by src/node_postmortem_metadata.cc to calculate
// offsets and generate debug symbols for BaseObject, which assumes that the
// position of members in memory are predictable. For more information please
// refer to `doc/guides/node-postmortem-support.md`
friend int GenDebugSymbols();
friend class CleanupHookCallback;
template <typename T, bool kIsWeak>
friend class BaseObjectPtrImpl;
v8::Global<v8::Object> persistent_handle_;
// Metadata that is associated with this BaseObject if there are BaseObjectPtr
// or BaseObjectWeakPtr references to it.
// This object is deleted when the BaseObject itself is destroyed, and there
// are no weak references to it.
struct PointerData {
// Number of BaseObjectPtr instances that refer to this object. If this
// is non-zero, the BaseObject is always a GC root and will not be destroyed
// during cleanup until the count drops to zero again.
unsigned int strong_ptr_count = 0;
// Number of BaseObjectWeakPtr instances that refer to this object.
unsigned int weak_ptr_count = 0;
// Indicates whether MakeWeak() has been called.
bool wants_weak_jsobj = false;
// Indicates whether Detach() has been called. If that is the case, this
// object will be destroyed once the strong pointer count drops to zero.
bool is_detached = false;
// Reference to the original BaseObject. This is used by weak pointers.
BaseObject* self = nullptr;
};
inline bool has_pointer_data() const;
// This creates a PointerData struct if none was associated with this
// BaseObject before.
inline PointerData* pointer_data();
// Functions that adjust the strong pointer count.
inline void decrease_refcount();
inline void increase_refcount();
Environment* env_;
PointerData* pointer_data_ = nullptr;
};
// Global alias for FromJSObject() to avoid churn.
template <typename T>
inline T* Unwrap(v8::Local<v8::Value> obj) {
return BaseObject::FromJSObject<T>(obj);
}
#define ASSIGN_OR_RETURN_UNWRAP(ptr, obj, ...) \
do { \
*ptr = static_cast<typename std::remove_reference<decltype(*ptr)>::type>( \
BaseObject::FromJSObject(obj)); \
if (*ptr == nullptr) return __VA_ARGS__; \
} while (0)
// Implementation of a generic strong or weak pointer to a BaseObject.
// If strong, this will keep the target BaseObject alive regardless of other
// circumstances such as the GC or Environment cleanup.
// If weak, destruction behaviour is not affected, but the pointer will be
// reset to nullptr once the BaseObject is destroyed.
// The API matches std::shared_ptr closely.
template <typename T, bool kIsWeak>
class BaseObjectPtrImpl final {
public:
inline BaseObjectPtrImpl();
inline ~BaseObjectPtrImpl();
inline explicit BaseObjectPtrImpl(T* target);
// Copy and move constructors. Note that the templated version is not a copy
// or move constructor in the C++ sense of the word, so an identical
// untemplated version is provided.
template <typename U, bool kW>
inline BaseObjectPtrImpl(const BaseObjectPtrImpl<U, kW>& other);
inline BaseObjectPtrImpl(const BaseObjectPtrImpl& other);
template <typename U, bool kW>
inline BaseObjectPtrImpl& operator=(const BaseObjectPtrImpl<U, kW>& other);
inline BaseObjectPtrImpl& operator=(const BaseObjectPtrImpl& other);
inline BaseObjectPtrImpl(BaseObjectPtrImpl&& other);
inline BaseObjectPtrImpl& operator=(BaseObjectPtrImpl&& other);
inline void reset(T* ptr = nullptr);
inline T* get() const;
inline T& operator*() const;
inline T* operator->() const;
inline operator bool() const;
template <typename U, bool kW>
inline bool operator ==(const BaseObjectPtrImpl<U, kW>& other) const;
template <typename U, bool kW>
inline bool operator !=(const BaseObjectPtrImpl<U, kW>& other) const;
private:
union {
BaseObject* target; // Used for strong pointers.
BaseObject::PointerData* pointer_data; // Used for weak pointers.
} data_;
inline BaseObject* get_base_object() const;
inline BaseObject::PointerData* pointer_data() const;
};
template <typename T>
using BaseObjectPtr = BaseObjectPtrImpl<T, false>;
template <typename T>
using BaseObjectWeakPtr = BaseObjectPtrImpl<T, true>;
// Create a BaseObject instance and return a pointer to it.
// This variant leaves the object as a GC root by default.
template <typename T, typename... Args>
inline BaseObjectPtr<T> MakeBaseObject(Args&&... args);
// Create a BaseObject instance and return a pointer to it.
// This variant detaches the object by default, meaning that the caller fully
// owns it, and once the last BaseObjectPtr to it is destroyed, the object
// itself is also destroyed.
template <typename T, typename... Args>
inline BaseObjectPtr<T> MakeDetachedBaseObject(Args&&... args);
} // namespace node
#endif // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
#endif // SRC_BASE_OBJECT_H_
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